Components of Accumulated other comprehensive loss (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	$ (153,155)		$ (166,815)
Income tax effect	14,475	[1]	15,623	[1]
Accumulated other comprehensive loss	(138,680)		(151,192)
Defined benefit plans liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	(139,426)		(153,225)
Income tax effect	14,663		15,784
Equity in investee other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	(12,712)	[2]	(12,712)	[2]
Income tax effect	436		488
Unrealized loss on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), before Tax	(1,017)		(878)
Income tax effect	$ (624)		$ (649)

[1] The allocation of the income tax effect to the components of other comprehensive income is as follows: September 30, 2013December 31, 2012Defined benefit plan liabilities$14,663$15,784Equity in investee other comprehensive income436488Unrealized loss on financial instruments(624)(649)

[2] The amount includes our equity in the other comprehensive income of Mt. Holly Aluminum Company.